Archaeologists know that the ground they examine can be literally rather shifty. The reasons for this can be disturbing, beastly and even childish.

For many an archaeologist, the greatest treasures are artefacts - "objects produced or shaped by human workmanship", as the dictionary puts it. The exact location of an artefact can be as important as the thing itself. In a dirt heap, what is next to what - and especially, what is on top of or below what - can impart telling information.

Archaeologists have it tough, though, because things do move around underground. Sometimes this is due to the actions of burrowing animals. Over the years, archaeologists have cautioned each other to beware of ants, termites, earthworms and rats and other rodents. A recent report from South America points out that: "There is, however, one animal that despite its regional ubiquity and notable burrowing behaviour has received little attention: the armadillo."

Writing in Geoarchaeology, Astolfo Gomes de Mello Araujo of the Universidade de São Paulo, and his colleague José Carlos Marcelino go into detail. "Although it seems clear that armadillos can move archaeological materials upward," they write, "previous studies have not considered whether they move artefacts downward."

The scientists conducted an experiment with armadillos in an underground dirt heap at the São Paulo zoo. They stacked coloured, flaked stones and bits of ceramic into layers, then let the animals have their way.

The armadillos were impressive object-movers. Gomes de Mello and Marcelino proudly report that: "Some of our findings have never been reported in the literature, such as the fact that armadillos can translocate artefacts downward to great depths as well as expel them towards the surface."

To a naïve non-archaeologist, such concerns may seem like child's play. But for good archaeologists, child's play is sometimes a serious problem.

Norman Hammond and the then infant Gawain Hammond illustrated this by doing an experiment. The older Hammond is a professor, now based at Boston University. The Hammonds' report, Child's Play: A Distorting Factor in Archaeological Distribution, appeared in 1981 in the journal American Antiquity.

The elder Hammond created an artificial trash pile one metre in diameter. He stocked it with wine jars, liquor bottles and beer cans. The younger Hammond was then permitted to play briefly in the pile. The report concludes: "The interpolation of 'child-play' may profoundly modify the initial archaeological pattern, and transmit it into an arbitrary pattern with an unrelated structure. The causes of this change must be allowed for in investigations of artefact." (Thanks to T Gill and N Hammond for bringing these to my attention.)

· Marc Abrahams is editor of the bimonthly magazine Annals of Improbable Research (www.improbable.com), and organiser of the Ig Nobel Prize